1. Field of the Invention
The present invention relates to a process for the production of a very thick, shaped, "laminated plastic", as well as to a machine for carrying out said process, and the product obtained thereby.
2. Description of the Prior Art
Laminated plastic is nowadays a product which is widely spread on the market. For producing the same, some sheets of Kraft paper weighing 100-150 g/sq.m., imbued with phenolic resin and, usually, at least one sheet of decorative paper weighing 100-120 g/sq.m., imbued with melaminic resin, are laid one upon the other and this pack of sheets is hot-pressed up to full polymerization of the resins.
One thereby obtains a flat sheet, actually called "laminate" owing to its characteristics of resemblance to a thin foil of high superficial hardness, resistance to stresses and sufficient flexibility.
Such plastic laminates are actually produced in different thicknesses, generally between six tenths of a millimeter and fourteen to sixteen tenths of a millimeter, and they have the desired flexibility--in spite of their hardness and strength--thanks to the very fact that their thickness is so reduced.
The plastic laminates produced at present have the outer surface showing the most varied decorative effects. If the superficial decorative sheet is of light colour, a sheet of barrier paper is usually interposed between the same and the underlying sheets of Kraft paper, so as not to let through the dark colour of said Kraft paper sheets.
The most widespread use of these plastic laminates is in carpentry, for lining furniture, particularly--but not exclusively--kitchen furniture, due to the actual characteristics of hardness and of resistance to wear of their surface.
By making full use of these characteristics it is in fact possible to obtain highly strong and long lasting furniture, even starting from panels of pressed shavings, instead of wooden panels, since plastic laminate, applied on the whole surface of the panel, is apt to give to this latter also a structural strength.
According to the most known technique, plastic laminate is cut to size and applied (glued) on each of the surfaces of the wooden panel, and trimmed along the edges. This technique suffers however from some drawbacks:
to start with, it is a relatively expensive technique, with great employment of labour for the work of cutting to size, of gluing the laminate onto the panel and of trimming the edges; PA1 moreover, due to the fact that kitchen furniture is particularly subjected to strong humidity and to frequent wetting, it may easily happen, after a relatively short period of use, that the laminate becomes unglued from the panel; PA1 finally, due to the modest flexibility of the laminate, even where its thickness is very reduced, it is impossible to line therewith surfaces having an emphasized curvature. PA1 to start with, because in a furniture panel--as for instance the rest or working surface of a piece of kitchen furniture--there are at least eight long edges, only two of which may eventually be protected in the aforespecified manner; PA1 furthermore, because the surface of the post-forming laminate is less resisting to wear or to cutting in that, as said, the polymerization of the resins is not complete. PA1 a pack of at least thirty Kraft papers imbued with phenolic resin is formed, PA1 said pack is laid onto a first part of a mold, shaped with bending lines parallel to a main axis of said mold, the sheets being seamed one onto the other at least along one of the edges parallel to said main axis, and PA1 the mold is closed according to a diagram of pressures which comprises at least an initial closing and preheating phase, under a minimum constant pressure and with a rising temperature of the pack of papers, and a second processing phase at a substantially constant temperature and with an increasing closing pressure.
To eliminate these drawbacks at least partly, it has already been proposed to produce "post-forming" laminates. They are flat laminates, substantially similar to those described hereabove, but wherein the polymerization of the resins (under pressure and heat) is not completed. These laminates may then be subjected--at a moment subsequent to their formation and therefore even just before they are applied --to a bending operation, so as to acquire even small bending radiuses, for instance of 15 to 20 mm.
This technique hence allows for instance to line, with a single piece of laminate, the major surface of a wooden panel and the surface of one side being connected thereto through a rounded chamfering. One thereby obtains, in addition to a special aesthetical effect, a protection of the edge joining said two surfaces, since in correspondence of that point, the lining has no interruptions.
The advantage obtained with post-forming laminates is however relatively modest: